Transmission regulation



Nov.. l, 1932.

s. BRAND' TRANSMISSION REGULATION Filed May 17, 1930 ATTORN EY Patented Nov. l, 1932 UNED STATES F1-Er @mcs i isi/Mincir BRANncr YoNKERs, NEW YORK.. AssIGNoR To` AMERICAN TELEPHONE AND frELEGRArH COMPANY, A oonronA'rIoN or'NEw YORK TRANSMISSION `nrxeuitA'rioN Application mea may 17, 1930. semi 110.453,284.

sion characteristics by changes of tempera-` ture, they transmission characteristics being a loffunction'of theifrequency of the transmitted.

current.- In Certain types of cables, at least,

field measurements show that an increase of temperature, forinstance, produces an increase of transmission loss at the low and p-intermediate frequencies vand that this change of transmission varies with frequency change, passing through zero fat a certain relatively high frequency'and becoming a negative increment in loss at the higher frequencies.

The principal object of the invention is to provide-for transmission regulation which will offset the variations mentioned above and produce a substantially flat transmissioncharacteristic over the normal range of temperatures and a wide range of frequencies.

In general I accomplish theabove-stated object Aby introducing a Vtransmission-frequency distortingimpedenace to give a gain characteristic of suitable form and simul- 'taneo'uslyi i introducing an adjusting impedance free from transmission-frequency distortion, as will be more fully disclosed hereinafter.

I do not claim as my invention the broader idea of introducingk a combination of adjustable impedances and adjusting these impedances in accordance with the temperature and with the frequency characteristic of the transmission medium; this was proposed be- 'fore the conception of the present invention.

I have found, however, that the methods and arrangements described and claimed herein resultin certain cases, at least-in satisfactory transmission regulation with the maximum of simplicity and economy.

My invention will be understood by those skilled in the art when the following description isread with reference to the accompanying drawing, of which- 59 Figure 1 shows diagrammatically a circuit `serve thepurposeof making clearjthe true `a shunt comprising the inductance L, the

arrangement for producing the transmissionfrequency distorting adjustment between the stages of a vacuum tubeV repeater;`

Fig. 2l shows curves illustrating the effect Y of the arrangement of Fig-T1;v y

Fig. 3 shows diagrammatically a desirable circuit arrangement 'for producing, in the case of a vacuum tube repeater, both the transmission-frequency .distorting veffect and the gain-adjusting non-distorting e'ect; and Fig. 4' shows curves indicating the desired ffect 'obtained by using the arrangement of 1g. 3. x It is to be understood that Figs. l and 2 nature of my improvement, but donot by themselves illustrate the inventionl in its complete aspect. l Y

Fig-jl, there is shown a repeater comprlsing` the vacuum tubes VT1 and T2, inserted in a transmission line. Between the tubes T1 vand Tgis` apotentiometerl? comprising a-.plurality of rsistances and a plurality of condensers asshown. Associated with this'k combination of Vresistances .and capacities is capacity VG and the resistance R. It will be understood, of course, Ithat the particular.v arrangement and lthe values of these impedance elements will vary withl the'particular circuitseinployedv andthe particular transmission' problems presented. The effect of the introduction of such an impedance .arrangementv in the'transmission circuit is, however, indicated in Fig. 2 of the drawing. The curves ZT and B correspond to the zero, top andV bottom steps, respectively, ofthe potentiometer setting according to temperature,the zero step representing, for instance, Fahrenheit. At this temperature, let it be assumed, it is found that the transmission characteristic is Asubsoi ly, ther potentiometer'Pat the ltop step setloe p ting, for instance, must introduce some such characteristic as that represented by curve T. It will be noted that the Veffect is to introduce a gain which is relatively large at U the lowerfrequencies and decreases as the frequency increases. Further, if the. shape of curve yTis such that the transmission characteristic of the system remains flat after. these changes have been madewthere must beL a net change'of lossat all frequencieswhich" is independent of'frequency sinceVVV the curve T does not cross zero. Likewise thecurve B corresponding to the bottom step/does not' pass through zero within the range offrequencies to be regulated. In order to take carefofthis -diiiiculty, I employ somesuch arrangement as that shown in Fig. 3. f In Fig. 3, as inFig. 1,- there is shown a two# stage vrepeater. with; tubes *T1V and T2 and a l .potentiometer P- between the tubes, this Apotentiometer having resistances, 'condensers and the shunt comprising the inductance L,

the capacity C 'and the' resistance R.' A sec` ond impedance network takestheform of a potentiometer P connected into the input circuitV of the A. repeater. This potentiometer P is'specilically shownas 'a simple' resistance potentiometer. It will be understood, Yof course, that it may, like the potentiometer V1:', take `otheraforms in accordancev with the particularrequirements. The essential feature is that it introduces no transmission-frequency distortion. Accordingly', with both impedance networks in the circuitjthe result will. 'be the introduction of 'a transmission adjustment such as thatiindicated-in Fig. i

(with reference to'Fig' 2).. It will' be noted I that 'the curverZ, corresponding'to the z ero step, is flat, and thatthe curves T "and B,

.corresponding to the-top and-bottom steps, respectively, .have the same curvatures as curves T and vI,`respectively`, of 'Fig'. 2; the characteristics have, however, been adjusted to pass through Zero-within therangeo'f'fres quencies tobe regulated, and thus they giveV the desiredoflsetto the negative increment in loss at the higher frequencies,^which has been discussedY above.v

It will be' noted in Figs?)V that the two po- Vtentiometers P andvP` are arranged tostep inyopposite directions when one -increases thel loss, the other should simultaneously step to decrease the loss'.V Y This arrangement will meet the Ausual'-requirements.l Such simul;

' taneous and opposite adjustments of impedance may,vof course, be brought about by anysuitable meansfor instance, the top steps may be located as shownand switching means-such as master relays may give the simultaneous control of the potentiometers.

Y.While the e' invention has been Vdisclosed specifically for the purpose of illustration, it is vto vbe understood that its true scope is determined by thesappended claims.

-across Vsaid repeater, said second potentiometer having a plurality of steps to correspond to temperaturevariation and being so constructedflthat it introduces no transmis-1- sion'-frequency distortion', and* means for tiometers.

2. In a'transmission circuit in whichllthe transmission loss varies with tempera-ture and also :with the Vfrequency rof the transmitted currents, arepeater comprising a plurality of vacuum.rtubes,'a potentiometer between two of'said vacuum tubes having a plurality simultaneously controlling the'two poten-l ofsteps to-fcorrespond to'temperature variation, a shunt impedance connected across said potentiometer, said -xpotentiometer and said shunt impedance -serving to produce a gainv variable with the' frequency ofthe transmitted currents, a second potentiometer yin kthecirc'uit ahead oflthe rstof said two vacuumM tubes, said second potentiometer" havingv a plurality offstep's'tocorrespond to temperature 5 variation and i being so con-y structed-that itintroduces no trans-mission-v frequency distortion, and means forl simultaneously controlling'thetwo potentiometers f tof introduce?transmission'feffects in Vopposite directions. Y

`In testimony whereof,"I'have signed my Maywealname to this specificationthis 15th day of `SMART BRAND.

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